Numerous mutations that are associated with both syndromic and non-syndromic hearing impairment have been found in pendrin and prestin, which are members of the SLC26 family. In most cases, it is not clear how these mutations disrupt the normal function of pendrin and prestin proteins. Characterization of such disease- associated mutations in human patients is, therefore, urgently needed to understand the underlying pathology. Data collected in these experiments will further our understanding of the molecular mechanisms of normal pendrin and prestin on their transport and motor functions. Using this information, we will develop mechanistic models of the proteins, which are expected to generalize to all other SLC26-family members, and could be exploited to develop remedies against disease-causing mutations found in the SLC26 family of proteins in the future. Aims 1 and 2 are designed to determine the effects of disease-associated missense mutations reported for pendrin (Aim 1) and prestin (Aim 2) on their anion transport and voltage-dependent motor functions using recombinant proteins heterologously expressed in cell lines. Aim 3 will develop mechanistic models that explain transport (pendrin) and motor (prestin) functions based on the results obtained in the preceding Aims. In addition, we will carry out electrophysiological measurements to dissect the kinetics of prestin's motor activity. Standard molecular biological methods will be used to generate mutated protein constructs whose functional assessment will be performed using cell lines (in vitro). Animals will not be used in this study. Taken together, the proposed research will not only fill the gap between our current knowledge of disease-associated mutations and their functional consequences, but also help elucidate detailed molecular mechanisms of SLC26 family of proteins.